Add random util

Add a user-friendly tool to generate random numbers.

app/meson.build

@@ -37,6 +37,7 @@ src = [
     'src/util/net_intr.c',
     'src/util/process.c',
     'src/util/process_intr.c',
+    'src/util/rand.c',
     'src/util/strbuf.c',
     'src/util/str.c',
     'src/util/term.c',

app/src/util/rand.c

@@ -0,0 +1,24 @@
+#include "rand.h"
+
+#include <stdlib.h>
+
+#include "tick.h"
+
+void sc_rand_init(struct sc_rand *rand) {
+    sc_tick seed = sc_tick_now(); // microsecond precision
+    rand->xsubi[0] = (seed >> 32) & 0xFFFF;
+    rand->xsubi[1] = (seed >> 16) & 0xFFFF;
+    rand->xsubi[2] = seed & 0xFFFF;
+}
+
+uint32_t sc_rand_u32(struct sc_rand *rand) {
+    // jrand returns a value in range [-2^31, 2^31]
+    // conversion from signed to unsigned is well-defined to wrap-around
+    return jrand48(rand->xsubi);
+}
+
+uint64_t sc_rand_u64(struct sc_rand *rand) {
+    uint32_t msb = sc_rand_u32(rand);
+    uint32_t lsb = sc_rand_u32(rand);
+    return ((uint64_t) msb << 32) | lsb;
+}

app/src/util/rand.h

@@ -0,0 +1,16 @@
+#ifndef SC_RAND_H
+#define SC_RAND_H
+
+#include "common.h"
+
+#include <inttypes.h>
+
+struct sc_rand {
+    unsigned short xsubi[3];
+};
+
+void sc_rand_init(struct sc_rand *rand);
+uint32_t sc_rand_u32(struct sc_rand *rand);
+uint64_t sc_rand_u64(struct sc_rand *rand);
+
+#endif